1. Field of the Invention
The present invention relates in general to apparatus and method for disposal of putrescent waste material, and in particular the continuous bio-conversion of putrescent waste material.
2. Description of Related Art
Society generates huge quantities of putrescent waste:
farm waste from plants, animals, and birds;
food storage waste;
commercial food preparation waste;
kitchen waste (institutional, restaurant and domestic);
plate waste; and
human waste.
The production of organic compost for municipal refuse or garbage is well known. For example, U.S. Pat. No. 5,082,486 filed on Nov. 16, 1990 by Glogowski teaches a method for the production of organic compost comprising the following steps:
1. shredding the refuse;
2. adding water to saturation;
3. adding earthworms;
4. keeping the water content at more than 80% during at least 30 days; and
5. keeping the mixture at a temperature from 0-54xc2x0 C. and with a moisture of at least 45% during more than 4 months.
Such a method is not suitable for continuous treatment of large amounts of putrescent waste. Furthermore, the separation of earthworms from the treated waste materials is very difficult.
The prior art suggests various types of bio-conversion facilities for facilitating the production of useful animal products from putrescent waste material. One device and associated method relates to the continuous treatment of large amounts of humid putrescent waste materials by means of fly larvae. Thus, after a relatively short period of a few days, the putrescent waste is converted into a slightly moist odor-free compost. After treatment of the waste materials, the use of fly larvae allows for separation of the larvae from the waste. Live or dehydrated larvae constitute an excellent feed stock for fish and poultry, but the larvae can also be used for the production of by-products such as protein meal, fats, chitin, and chitosan. It has been observed that when using fly larvae for the treatment of putrescent waste materials, it is possible to induce them to crawl out of the waste by exposing the waste to an illumination, preferably together with a heating, especially an infrared illumination, whereby the separation of the larvae out of the putrescent waste is obtained by the larvae themselves.
The larvae that we have chosen for this waste disposal process is the larvae of the black soldier fly (Hermetic illucens). It is a tropical fly indigenous to the Americas, from the southern tip of Argentina to Boston and Seattle. During World War II, the black solider fly (BSF) spread throughout the world. Today, it can be found in China, Japan, Korea, the Philippines, Vietnam, Laos, Cambodia, Thailand, Indonesia, Singapore and even Australia. Unlike many other flies, BSF adults do not go into houses; they do not have functional mouth parts; they do not eat waste; they do not regurgitate on human food; and therefore, they are not associated in any way with the transmission of disease. BSF adults do not bite, bother or pester humans in any way. Even though BSF larvae have been known to survive inside the human gut if swallowed whole, this is extremely rare and poses absolutely no danger to humans.
BSF adults are around only for the purpose of mating and laying eggs. The adults congregate in small numbers near a secluded bush or tree in order to find and select a mate. After mating, the female searches for a suitable place to lay her eggs. She produces about 900 eggs in her short life of 5 to 8 days. (Housefly adults, by contrast, live up to 30 days.) Half of the population of adult black soldier flies (the males) never go near waste, since males to not lay eggs. Actually, the females prefer not to lay their eggs upon the waste, but either above or to the side of the waste. In this way, the eggs have a far better chance of surviving. The eggs are very slow in hatching (102 to 105 hours). The newly hatched larvae then crawl or fall onto the waste and begin to eat and digest it with amazing speed.
Under ideal conditions, it takes about two weeks for the larvae to reach maturity. If the temperature is not right (above 21xc2x0 C. or 70xc2x0 F.), or if there is not enough food, this period of two weeks may extend to four months. This ability of the BSF larva to extend its life cycle under conditions of stress is a very important reason why it was selected for this waste disposal process. BSF larvae pass through five stages or instars. Upon reaching maturity, the larvae are about 25 mm (1 in.) long, 6 mm (0.24 in.) in diameter, and they weight about 0.2 gm (0.0014 oz.). The larvae are extremely tough and robust. They can survive under conditions of extreme oxygen deprivation. It takes them, for example, approximately two hours to die when submerged in rubbing alcohol. They can be subjected to several 1000 g""s of centrifugation without harming them in any way. BSF larvae are strong, robust, flexible, adaptable, and very easy to manage.
But their greatest attribute, of course, lies in their ability to eat and digest raw waste. They can devour, for example, a large, raw Irish potato in just a few hours. Many species of flies cannot eat raw waste, unless the waste first undergoes a certain level of bacterial decomposition. Not so with the larvae of the black soldier fly. Since the BSF larvae have very large mouth parts, they can shred and ingest raw waste far more efficiently than any other known species of fly. The only things that they cannot shred are large pieces of food waste of a high cellulosic, calcium or chitin content, such as the shell of a coconut, crab or shrimp, or a piece of bone. Therefore, it would be advisable for us to shred these tough objects to a grain size small enough to be ingested by the BSF larvae. This also assures a relatively uniform grain size with respect to the larvae residue.
BSF larvae have amazing appetites. In a small experiment conducted in Texas over a period of one year, it was determined that the BSF larvae can digest over 15 kg of raw waste per m2 of disposal per day (approximately 3 lbs./ft2/day). As a sidebar, it is also noted that within a single day this 15 kg of waste was reduced to less than 1.5 kg of larval residue. In other words, an optimal bio-conversion processes utilizing the BSF may expect a 90% reduction in the weight and volume of the food waste within a 24-hour period. On the surface of the disposal unit, one finds a thick layer of actively feeding larvae in all stages of growth. The moment the food waste is deposited into the unit, it is digested by the BSF larvae long before it has had a chance to degrade complex organic compounds. Therefore, most of the nutrients and energy within the waste are conserved and recycled with the help of the BSF.
While actively feeding, the larvae secrete a chemical, more precisely an infochemical, that permits them to communicate with other species of flies. This infochemical or synomone allows them to tell other flies to stay away, that it makes little sense to lay their eggs within an area full of actively feeding BSF larvae. This interspecies communication is indeed very effective. In the vicinity of the disposal unit, we note the near absence of houseflies and all other flies that are a pest to humans. If only we could isolate this natural fly repellant produced by the BSF larvae! After about two weeks of feeding, the BSF larvae reach maturity. They turn from white to black, their mouth parts transform into a digger, they empty their guts of waste, they secrete an antibiotic to protect themselves from bacteria, and they set out in search of an ideal pupation site.
The BSF larvae will easily crawl over 100 meters (320 ft. +) in search of an ideal pupation site. An ideal pupation site must be free of the enormous bacteriological activity which characterizes the waste disposal area, free of small predators such as predatory mites and pseudo-scorpions, and free as well of large predators such as birds, rats and mice. Furthermore, an ideal pupation site is never simply out in the open. It must be a shaded, dry area providing refuge or cover for the mature pre-pupal larvae. BSF larvae are negatively phototactic (afraid of light), and therefore most of their migratory activity takes place at night. Their migration initially appears to be a random search for a way out of the waste. If a ramp of an upward inclination lies at the edge of the waste, they will make every effort to climb up this ramp.
As long as the ramp has an angle of less than 45 degrees, the BSF larvae have no problem exiting the waste. Such a steep angle makes it difficult for the larvae to drag or carry along any adhering residue, and it also serves as a barrier for the larvae of most other species of fly. Housefly larvae, for example, are not even able to climb a ramp of a 30-degree angle. If housefly larvae cannot get out of the disposal area, they cannot pupate, and if they cannot pupate, they cannot become adults and reproduce. The BSF waste disposal unit mounted with steep ramps serves as a very effective sink or trap for the larvae of just about every species of flies that ignores the chemical warning to stay away from the unit. Once trapped within the unit, the uninvited larvae and pupae eventually become one more food item for the hungry BSF larvae.
After crawling up the ramp, the BSF larvae will continue in search of an ideal pupation site. If the ramp discharges into a horizontal pipe, the larvae will crawl over this pipe, over relatively large distances, until they come to downspout that discharges into a bucket. BSF larvae are totally self-harvesting. They abandon the waste only when they have reached their final mature pre-pupal stage, and they crawl out of the waste into a container without any mechanical or human intervention.
42.1% crude protein
34.8% ether extract
7.0% crude fiber
7.0% moisture
1.4% nitrogen free extract (NFE)
14.6% ash
5.0% calcium
1.5% phosphorus
(Source: Newton, Booram, Barker and Hale, 1977)
Studies were conducted at the Coastal Plain Experiment Station in Tifton, Ga., to examine the suitability of BSF larvae as a feed source for channel catfish and tilapia. The test concluded that xe2x80x9csoldier fly larvae should be considered a promising source of animal protein in fish production.xe2x80x9d Taste tests were also conducted: xe2x80x9cResults of the taste tests indicated that fish fed soldier fly larvae are acceptable to the consumer.xe2x80x9d Vietnam produces large quantities of catfish, and BSF larvae could become a significant source of nutrients to the catfish industry in Vietnam. (See Bondari and Sheppard (1980), pp. 103 and 108).
Also, BSF larvae contain a high percentage of dry matter: 44%. The catfish industry in the United States buys approximately 600,000 TPY (tons per year) of catfish food at an average wholesale price of $550 per ton. If one dry ton of BSF larvae should have a value of $400 as a feed ingredient in catfish food, then one ton of food waste could generate the equivalent of about $40 in catfish food ($400*20%/2). If each transfer station received one ton of food waste per day, then this represents per transfer station approximately $40 per day, $1,200 per month, or $14,600 per year. But the value of BSF larvae is not limited to the catfish industry.
As a polysacharide, chitin is one of the most abundant substances within nature. Through a process of deacetylation, chitin can be made soluble in water. This soluble form of chitin is called chitosan, a polycationic carbohydrate polymer. Chitosan has a value ranging from $4,000 to $10,000 per ton, depending on purity and other quality specifications. Furthermore, it has been determined that the chitin content of BSF larvae on a dry basis is approximately 20.4%. If 80% of the BSF chitin converts to chitosan at a value of $4,000 per ton, then one ton of fresh larvae represents over $281 in chitosan alone.
If one ton of fresh larvae represents $133 of protein and fats, and an additional $281 in chitosan, then one ton of fresh larvae has a total value of over $400. To this must be added the value of the larval/redworm potting soil at approximately $100 per ton. At a conversion rate of fresh food waste into fresh larvae of 20%, then one ton of food has a value of about (400/5+10) $90. The entire effort to recycle food waste is driven by the value of the products and byproducts derived from this waste.
FIG. 1 is a flow diagram of a prior art bio-conversion facility for continuous treatment of putrescent waste by means of fly larvae in which the fly larvae actually eat the waste. Facility 100 is further described by U.S. Pat. No. 5,759,224 filed on Aug. 22, 1996 by Paul A. Oliver and is incorporated by reference herein in its entirety. Facility 100 comprises walls 101 defining fly larvae cultivation chamber 102 for the treatment of putrescent waste. A stack of at least two conveyor belt systems 108, each having a waste reception zone 108A, a treatment zone 108B in which the putrescent waste is more or less completely eaten by fly larvae, and an evacuation zone 108C, is designed so as to transport the waste and the fly larvae eating the waste from the reception zone 108A towards the evacuation zone 108C. A system 130 grinds putrescent waste material to be treated so as to form a pulp containing particles of more or less uniform grain size, the grain size being preferably smaller than the size of the mature fly larvae mouth, and a blending and holding tank 140 contains the ground putrescent waste. Pump 148 transfers the waste from the blending and holding tank 140 to paddle box 131. Variable speed control system 149 for pump 148 controls the discharge rate of waste into paddle box 131. A pipe or other transfer means 150 is used to transfer the ground waste from pump 148 into paddle box 131, the pipe or transfer means 150 being provided with heating system 144.
Valve 151 is mounted on pipe 150 to select sequentially the specific paddle box 131 and conveyor belt 108 that are to receive the waste. The distribution paddle box 131 has paddles that, in the preferred embodiment, turn in a direction opposite the flow of material so as to ensure a more or less even deposition of the ground putrescent waste down an inclined chute onto the central section of a long conveyor belt (80-100 meters), leaving the lateral surfaces of the conveyor belt free of waste. One or more distribution bags 110 contain an aqueous suspension of fly larvae eggs, the bags 110 being made preferably of plastic, and being connected to one or more tubes 145 through which the suspension liquid containing eggs drops onto the waste exiting the paddle box. A container with holes in the bottom could also be used to drip larvae onto the conveyor belt 108. A motor and speed reducer drives the conveyor belt 108; the motor being associated with a system well known in the art for controlling the speed of the conveyor belt 108. An air-conditioning system 112 controls the most appropriate temperature, humidity, and oxygen content in the fly larvae cultivation chamber (for example, between 28xc2x0 C.-38xc2x0 C. [82xc2x0 F.-100xc2x0 F.] between 30-90% relative humidity), depending on the species of fly larvae used. An air-scrubbing system 113 deodorizes the waste material leaving the fly larvae cultivation chamber in a well-known manner.
Infrared lamps 115 are located in evacuation zone 108C for inducing the larvae to crawl out of the waste. Two troughs 116, one on each lateral side of the conveyor belt (not shown), collect and transport the larvae falling or sliding from conveyor belt 108, each trough 116 having a water inlet (inlet 117) so as to create a high-speed water stream for transporting the larvae out of the trough, as well as an outlet (outlet 147) for evacuating the water and fly larvae. Transfer pipe 146 connects outlet 147 of a first conveyor belt trough to inlet 117 of a second conveyor belt trough, the second conveyor belt preferably being situated below the first. Pipe 118 through which the water stream with larvae flows toward a central rinsing and de-watering device 119 that may be, for example, a vibratory de-watering screen. Conveyor belt scraper 141 is used for scraping and cleaning the conveyor belt and for transferring the fly larvae residue onto chute 142. Centralized conveyor belt 143 receives waste from one or more waste chutes 142 and a storage area or surge bin (not shown) receives the waste from conveyor belt 143. A variable speed control system 123 is used to determine the speed or the intermittent movement of the conveyor belt (for example, if the larvae in the evacuation zone have not reached optimal maturation, the speed of the conveyor belt is reduced so as to increase the residence time of the larvae on the conveyor belt). System 132, shown in phantom lines in FIG. 1 and well known in the art, may be used for measuring the thickness of the waste deposited on the conveyor belt and controlling the amount of eggs or larvae to be added to the waste, so that the appropriate amount of eggs or larvae is added according to the thickness of waste on the belt, the system controlling, for example, the outlet of eggs or larvae from the distribution box 110. System 138, well known in the art, can be used for determining the presence of heavy metals or other contaminants in the waste, the system preventing the entry of contaminated waste into the blending and holding tank 140.
Paddle box 131 ensures an even deposition of the waste from a chute incorporated in paddle box 131, between distribution arms, on conveyor belt 108, but not over the entire width of the conveyor belt 108. This leaves the lateral surfaces of conveyor belt 108 adjacent to the lateral edges free of waste. The lateral surfaces are preferably about 10 cm in width and are provided with pins, needles, bristles, indentations, or holes, all of which may serve as a means for improving the detachment of waste particles adhering to the larvae crawling off the conveyor belt.
Upon reaching maturity, fly larvae naturally crawl out of the waste but, since they do not all reach maturity at exactly the same time, infrared lamps 115 are used for inducing the fly larvae to crawl out of the waste and off the conveyor belt in a synchronized and orderly manner. Even the direction in which the fly larvae crawl can be controlled by means of the graduated application of light and heat. Lamps 115 are preferably mounted in the form of a triangle, with one corner of the triangle intersecting the vertical plane passing through the middle line of the conveyor belt as shown so as to induce the fly larvae to crawl left and right of the middle line. When the conveyor belt is in motion, preferably all the lamps within the triangle are ON. When the conveyor belt is not in motion, preferably only some of the lamps are ON, electively providing a barrier across which the fly larvae would be reluctant to crawl. Instead the mature fly larvae move laterally on conveyor belt 108 into one of the two troughs 116 on each lateral side of conveyor belt 108 for collection. The larvae collected in the trough 116 can be sold as live fly larvae, but preferably they are further treated in a plant 126 for producing protein meat, chitin, chitosan and other valuable products.
The above-described device and associated method discloses producing a continual supply of mature fly larvae by maintaining co-existing populations of fly larvae at different states of development. Putrescent waste materials and fly eggs are continually added to a conveyor belt on which fly larvae mature. Simultaneously, larval residue is continually scraped from the moving conveyor belt at a point on the conveyor after the fly larvae have matured. The larval residue may then be processed using an alternative bio-conversion process. Alternatively, the larval residue may be composted or sold as product. However, the above-described device is rather complex and expensive to construct, maintain and operate. Furthermore, in situ operations involving the invention are not cost effective because the putrescent waste material must be deposited on the conveyor belt in a specified position. This insures that the fly larvae extract the maximum nutritional value from the waste material prior to the larval residue being scraped from the conveyor belt.
FIG. 2 is a cutaway diagram of another prior art bio-conversion facility for treatment of putrescent waste. The example described below has been developed by Craig Sheppard, Jeffery K. Tomberlin and Larry Newton at the National Environmentally Sound Production Laboratory at the College of Agriculture and Environmental Sciences at The University of Georgia. Facility 200 may also bio-convert putrescent waste by means of fly larvae whereby the fly larvae actually eat the waste material or bacteria which occurs on the waste, as discussed above with respect to facility 100 shown in FIG. 1. However, unlike facility 100, facility 200 depicted in FIG. 2 may be an in situ facility co-located with the putrescent waste material producing operation.
Facility 200 depicts the bio-conversion of putrescent wastes from caged laying hens at an egg laying facility. Each laying hen excretes an amount of putrescent waste material and the fly larvae feed on the hen waste. Cages 244 are suspended in a staggered arrangement above disposal volume 202 in such a manner as to expose a maximum area of cage floor mesh to disposal area 202. By configuring cages 244 in such an arrangement, waste falls from cages 244 directly into disposal volume 202, thereby eliminating the need to transport the putrescent waste material to disposal volume 202. In the present arrangement, cages 244 are arranged in four separate stacks with walkways 242 on either side of each stack. Walkways 242 extend the length of facility 200, as do cages 244.
Positioned below walkways 242, disposal volume 202 is subdivided by wall 208. At either side of disposal area 202 ramps 204 are positioned which lead to collection tubes 206. Collection tubes 206 are fabricated with longitudinal openings adjacent to ramps 204 (not shown), which run the length of collection tubes 206. As the laying hens in cages 244 deposit putrescent waste into disposal area 202 fly eggs are introduced. Fly larvae hatch from the eggs. When the fly larvae mature, the mature larvae surface from the putrescent waste in search of a more favorable environment to pupate. Fly larvae feed in only the top few inches of waste, but interestingly a population of fly larvae will tend to self regulate its numbers in order to extract optimal nutrition from each layer of waste prior to reaching the maximum feeding depth of the fly larvae.
Once the fly larvae reach maturity, the mature larvae crawl out of the putrescent waste material and onto the surface. The fly larvae attempt to navigate off of the surface of disposal volume 202 and away from the waste, as the larvae no longer need to feed on the waste. Facility 200 affords the mature larvae with only one avenue of escape from the putrescent waste, up ramps 204 and into collection tubes 206 where the larvae are collected and processed.
The deposition of waste material and collection of mature fly larvae continue unabated until larval residue must be collected from disposal area 202. Larval residue is the byproduct of the putrescent waste material after the bio-conversion process. The larval residue is of no value to the fly larvae and therefore must be removed from beneath cages 244 in order to provide additional space for new putrescent waste. However, it is impossible to remove only the larval residue without also removing the colony of fly larvae feeding in the top layers of the putrescent waste. The larval residue may be removed manually with shovels or may instead be collected by the bucket of a front-end loader and transported from disposal volume 202.
While facility 200 has the advantage of being less complex and expensive to implement than bio-conversion facility 100 in FIG. 1 discussed above, it has a disadvantage of being less efficient than facility 100. With respect to facility 200, disposal area 202 contains a colony of fly larvae in different stages of development, from newly hatched larvae to mature larvae because new fly eggs are introduced to the waste as larvae leave the disposal area. The colony is homogeneously distributed across the top few inches of putrescent waste disposal volume 202. However, each time the larval residue is removed from disposal area 202 an entire colony of fly larvae is destroyed. Production of mature fly larvae can only resume after new fly eggs are laid and their larvae mature. Other inefficiencies inherent with facility 200 are due to the loss of the top few inches of putrescent waste before it can be fully converted by the fly larvae and problems associated with re-regulating the population of larvae with the rate of deposition from the laying hens. Finally, the efficiency of larval crawl-off within facility 200 tends to be quite low, since the larvae, in such a large disposal unit, have great difficulties finding the ramps and exiting the waste.
Another prior art method and bio-conversion facility for the treatment of putrescent waste has been disclosed by the present inventor in U.S. Non-Provisional Pat. No. 6,391,620 titled xe2x80x9cDISPOSAL APPARATUS AND METHOD FOR EFFICIENTLY BIO-CONVERTING PUTRESCENT WASTES.xe2x80x9d U.S. Pat. No. 6,391,620 is hereby incorporated herein by reference in its entirety. U.S. Pat. No. 6,391,620 describes a waste disposal unit that takes advantage of the migratory behavior of the BSF larvae, commonly know as xe2x80x9ccommercial unit.xe2x80x9d
In the commercial unit, the waste is laid out in long disposal areas called xe2x80x9ctracks.xe2x80x9d A track could be several meters in width and several hundred meters in length. FIG. 3 is a diagram of a cross-section of disposal track, commonly know as a commercial unit, that is utilized in a bio-conversion facility for putrescent waste material is depicted in accordance with a preferred embodiment of the present invention. Waste material or more correctly, putrescent waste material and the bio-conversion living systems that feed on the putrescent waste material are confined in long disposal containers called xe2x80x9ctracksxe2x80x9d or xe2x80x9cdisposal tracks.xe2x80x9d Disposal track 300 encompasses a disposal volume, the cross-section of which is depicted by disposal area 302. Disposal area 302 is flanked by vertical curtain 310 which folds away from disposal area 302 forming ramp 304. Width w of disposal area 302 in disposal track 300 may vary from a few feet to approximately 20 feet and the overall width of disposal track 300 including ramps exceeds that. The length of a track may vary from a few feet to more than 1000 feet.
Flanking vertical curtains are further joined to front and rear sides (not shown), which delineate the disposal volume. Lateral support for the portion of vertical curtain 310 proximate the front and rear sides is provided by the sides, however, long runs of vertical curtain 310 require further support because the curtain lacks the structural integrity necessary to support large volumes of waste material. Therefore, in accordance with another preferred embodiment of the present invention, a series of lateral panels are positioned inside disposal track 300. Either end of every lateral panel 317 is connected to opposite vertical curtains flanking disposal area 302. Vertical curtains 310 are thus prevented from buckling outward under the stress of a heavy load of waste material. However, here again the force of the waste material on the lateral run of lateral panel 317 may introduce instability in lateral panel 317 so a series of longitudinal panels are interposed between the series of lateral panels. Longitudinal panel 319 runs parallel to vertical curtain 310 and may be connected to front and rear sides of disposal track 300. It is expected that both the lateral panels and longitudinal panels are securely fastened to one another, the vertical curtains and front and back sides by corrosion resistant fasteners or welding. Once secured, the sides, curtains and panels form a rigid, one-piece disposal track capable of withstanding the force exerted by the waste material and vibration resonance associated with excavating larval residue, is discussed in detail below.
Height h of disposal area 302 in disposal track 300 also varies depending on the feeding depth of the type of living system selected for the bio-conversion process and therefore, at a minimum height h must accommodate the living system. In accordance with a preferred embodiment of the present invention the minimum height h of disposal track 300 is equivalent to the combined feeding depth of the selected bio-conversion living system and the height of a larval residue excavation interval (the larval residue excavation interval will be discussed in detail below with respect to the scraper).
Ramp 304 extends approximately one foot at an uphill inclination of 15xc2x0-45xc2x0, however, these parameters are merely exemplary and may be modified depending on the lifecycle of the selected living system. Ramp 304 in the present example is intended for larvae-like organisms and may be omitted when disposal track 300 utilizes other living systems for bio-conversion. In the case of fly larvae, ramp 304 abuts collection tube 306. Collection tube 306 runs parallel and is attached to ramp 304 at longitudinal slit 307 which formed in the upper portion of collection tube 306. The slit is proximate to the upper extent of ramp 304. Downspout(s) 308 are positioned at predetermined intervals along collection tube 306 which are designed to act as a conduit to container 309 for trapping and holding the larvae. Container 309 is a convenient holding means temporary storage of live larvae prior to collection.
In accordance with a preferred embodiment of the present invention, vertical curtain 310 does not intersect the floor of disposal area 302; instead, residue excavation gap 312 is formed between the lower edge of vertical curtain 310 and the bottom of disposal area 302. The function of excavation gap 312 will be discussed in detail below. In further accordance with a preferred embodiment of the present invention, the floor of disposal track 300 is formed by under-pan 314, which is positioned beneath disposal area 302 of disposal track 300. Under-pan 314 may be supported by any expanse of ground or flooring having a level area capable of accommodating the area of under-pan 314. However, due to the need for residue excavation gap 312, under-pan 314 cannot support either vertical curtains 310 or the one-piece disposal track described above. Instead, vertical curtain 310 must be secured to pilings, or other similar support mechanisms (not shown), which are positioned outside the lateral extent of under-pan 314. Vertical curtains 310 or one-piece disposal track 300 may instead be suspended from an overhead framework. Whichever manner of support selected, residue excavation gap 312 must be maintained between vertical curtain 310 and under-pan 314.
Under-pan 314 supports the load created by putrescent waste and larval residue in the disposal area and provides a means for filtering water from the larval residue away from disposal area 302. In addition, under-pan 314 also serves to aerate the outgoing larval residue and elevates a scraper on a plane with gaps 312. This function will be discussed in greater detail below. In accordance with a preferred embodiment of the present invention, under-pan 314 is comprised of screen 316 supported longitudinally by prisms 318. Screen 316 may be composed of a plurality of layers of increasingly finer diameter filtration material. For example, an initial layer of screen 316 may be composed of a metal grid such as expanded metal commonly referred to as diamond mesh, which provides the necessary strength for supporting the waste in disposal area 302. In addition to the layer of expanded metal grid, screen 316 may comprise a second layer of finer diameter mesh applied over the metal grid. The diameter of the finer mesh determines the size of the particulate waste mater restricted from percolating into under-pan 314 with the filtrate. Depending on the strength and filtering properties of available meshes, screen 316 may be comprised of more than two mesh layers in order to accommodate the unique strength and filtration requirements for a particular bio-conversion application.
Screen 316 is supported by prisms 318 which are equally spaced along screen 316 by a predetermined amount and run lengthwise parallel to the length of disposal track 300. Note that the runoff of filtration fluids across prisms 318 will be channeled in troughs created by the space between adjacent prisms. Prisms 318 may be constructed from individual lengths of angle iron wherein each length of angle iron has the necessary dimensions to support screen 316 and the height adjacent the opening of gap 312. Of course, both screen 316 and prisms 318, as well as every other part of under-pan 314, must be either fabricated of corrosion-resistant materials or treated so as to resist the naturally corrosive properties of the putrescent waste and filtration fluids drained away by under-pan 314.
In accordance with other embodiments of the present invention, prisms 318 in under-pan 314 are replaced by a latticework of intersecting vertical partitions (not shown) which provide the necessary support for a scraper. However, because disposal track 300 may extend lengthwise for hundreds of feet, lengthwise runs of vertical partitions are intersected at right angles and run side-to-side for strength. Alternatively, this lattice of intersecting vertical partitions may instead be oriented at forty-five degree angles from vertical curtain 310. Any latticework structure must be provided with drainage or weep hole to allow runoff of filtration fluids to migrate toward a filtrate collection mechanism.
In operation, the waste is deposited onto the surface of the track where the larvae are actively feeding. On each side of the track there is a ramp 304, and the larvae, upon reaching maturity, crawl up ramp 304 and through longitudinal slit 307 in pipe 306 running alongside the track.
The commercial unit is ideal for handling specialized type of waste such as chicken waste. FIG. 2 depicts caged layers could be situated above disposal area 202 but alternatively could be suspended above a disposal track 300 as described in U.S. Pat. No. 6,391,620. As soon as the chicken waste is produced, falls directly into disposal area 302 of unit 300 to be consumed by the BSF larvae. With respect to chicken waste, BSF larvae remove 50% of the phosphorus, and they also effect a 75% reduction in the weight and volume of chicken waste. The greatly reduced chicken waste (dry, friable and odor-free) makes a wonderful organic fertilizer. The residue of the larvae is allowed to accumulate in the disposal track and is retained laterally by means of two curtains 310.
A larval evacuation pipe 306, ramp 304 and curtain 310 are suspended off floor and support screen 316. This leaves an opening of approximately 45 mm (1.77 in.) at the bottom of the curtain. The larval residue is easily scraped and extracted through this opening and deposited to one side of the disposal track. A small 150 mm (5.91 in.) wide conveyor belt, running parallel to the disposal track, completes the evacuation of the residue.
The extraction of the larval residue is accomplished by means of a scraper. The length of the scraper corresponds to the width of the waste disposal track. The scraper travels underneath the disposal area, moving from one longitudinal end of the disposal track to the other. When the level of larvae and fresh waste rises above the base of the ramp, the scraper is set in motion, extracting approximately 50 mm (1.97 in.) of larval residue. The concept is quite simple: waste is deposited on the surface of the disposal track, and larval residue is periodically removed from the bottom. The scraper is fabricated out of a chain fitted with blades. As the scraper advances underneath the track, the blades evacuate the larval residue at a 90-degree angle to the longitudinal axis of the track. The following drawing shows how the scraper is fabricated.
While various types of bio-conversion facilities for the treatment of putrescent waste are known in the prior art, each has several disadvantages making them unsuitable for some situations. For example, each of the above-described systems requires a fairly sophisticated implementations, including significant capital, specialized equipment and a relatively skilled personnel for operating the facility. Each of the facilities described above could be considered moderately mechanized and as such require a specific floor plan for efficient bio-conversion operations. Additionally, depending on the level of mechanization, the skill level of the labor force, as well as the initial capital expenditures both increase with the level of mechanization. Each of the above described have bio-conversion facilities also have the additional disadvantage of needing a rather large surface footprint for the amount of area actually devoted to the bio-conversion process. Thus, the prior art bio-conversion facilities generally do not make efficient use of land area. These shortcomings make prior art bio-conversion facilities generally unsuitable for location in confined spaces. Moreover, given their inefficient use of surface area and need for moderately skill operating personnel combined with their high initial capital costs, in many situations these facilities are unsuitable for many rural and underdeveloped regions.
The present invention is directed to an apparatus for efficiently bio-converting putrescent wastes to a more usable form and corresponding method for using the apparatus. The present xe2x80x9cdomesticxe2x80x9d unit does not utilize a motor nor does in contain any moving parts. Instead, the present domestic generally comprises a generally rounded container with one or more ramps on the inside of the container. In the two-ramp embodiment, the two ramps begin at the bottom of the container and spiral up to the top of the container, where they adjoin a discharge pipe. In operation, the putrescent waste is deposited into the domestic unit container. Mature larvae have only one avenue of escape from the putrescent waste, up the ramps and into discharge pipe and onto collection tubes where the larvae are collected and processed. When the container fills up with larval residue, the larvae are removed from the container, the container is emptied of residue, and the larvae are put back into the container. Because the container may be fabricated in any size, from a wide variety of materials, smaller containers can be manually tended.